1. Field of the Invention
The present invention relates to the field of magnetic disc enclosures and, more particularly, relates to air circulating systems for cooling and decontaminating air in the interior of such enclosures.
2. Description of the Prior Art
In high speed data processing systems, information is frequently recorded on magnetic discs for storage and rapid retrieval. Many of these discs are arranged axially with a plurality of similar discs attached to a common spindle. The spindles and the spindle mount drive the discs in rotation about the axis of the spindle. Such packages are frequently called storage files.
Such coaxial storage files are sealed within an enclosure. The enclosure frequently has generally cylindrical sides with a top and a bottom facing opposite sides of a circular disc. The generally cylindrical exterior frequently has a center coincidental with the spindle axis.
Magnetic heads mounted on a carriage are disposed within the enclosure for reading and writing digital bit information on the magnetic discs. Hereinafter is this description, the relationship of the present invention to magnetic disc files will be described.
The discs are rotated at high speed, frequently at approximately 3000 rounds per minute. Air inevitably begins a flow within the enclosure. The flow is generally in a spiral outward from the spindle or axis to the peripheral circumference of the magnetic discs themselves. One component of the air flow is radially outward from the axis. Friction between the spinning disc and the air immediately adjacent thereto is one cause of the flow. Impurities suspended in the air begin moving as the flow pattern develops within the enclosure. Such impurities have been known to interfere with the reading and writing of the information on the disc by obstructing the free motion of the magnetic head or by impairing the clearance between the head and the disc surface.
It has been known in the past to recirculate the enclosed air from the circumference or periphery of the disc. A filter within a recirculating plenum is designed to remove impurities and contaminants in order to increase the usable lifetime of the rotating drive assembly and to prevent interference with the writing and reading of the disc by the magnetic head.
In this regard, attention is directed to Buslik, U.S. Pat. No. 3,710,357, and Cuzner, et al., U.S. Pat. No. 3,849,800. These patents disclose air recirculated from outside of a magnetic disc through a filter and returned into the magnetic disc enclosure at a point somewhat offset from the axis. Also offset from the axis is another filter, a breather filter, which has the function of cleaning any air tending to enter the enclosure due to air temperature changes, or to replace air leaked from the cabinet. Such an off-axis breather filter most often results in a pressure differential across contaminant containing bearings that is unfortunately opposite that desired, when the air immediately inside the filter is at ambient pressure. This characteristic will be discussed in greater detail below. Such and similar arrangements have met with varying degrees of success, but certain problems remain when using them.
It has been found that having the breather filter offset from the axis of rotation allows the pressure to be much more negative relative to the outside ambient pressure at the axis than if the filter were located at that axis. The influence of such a negative pressure has the effect of drawing into the enclosure impurities from and through the axially positioned spindle bearings.
It is apparently impossible or impractical to completely seal the spindle bearings to prevent air flow through the bearings. The enclosure having such a negative pressure thus inevitably receives contaminants.
The air recirculation system, while being acceptable for single disc units, poses potential problems in multidisc applications. The air entering the enclosure from the filter plenum is cleaner and possibly warmer or cooler than the average air in the enclosure.
In a multidisc system with the air recirculation below the bottom disc, axial contamination and temperature gradients can exist. Contamination gradients cause less protection for the heads and discs furthest from the recirculation system. Temperature gradients affect the accuracy with which the read-write heads can be positioned over a previously written track.
It is sought to provide an air recirculation system for magnetic disc enclosures which feeds the movement of contaminated air in an axially symmetrical fashion to a peripheral filtering arrangement. It is also sought to achieve a minimizing of the influx of new contaminants into to enclosure by proper pressure control utilizing as much of the necessary disc movements as possible.